Air filters are employed in manufacturing operations, such as in textile manufacturing plants, to remove contaminants, such as dust, lint and other airborne fibrous materials from the environment, not only for the health, comfort and safety of operator personnel, but also to protect processing equipment and other air conditioning equipment employed in connection with the manufacturing operation. Because of the large volume of air which must be handled and effectively filtered, industrial air filter units typically comprise relatively large cylindrical drums having a large peripheral filter surface area. Air in the immediate and/or surrounding areas of processing equipment is passed at a desired flow rate into the interior of the drum and outwardly through the filter medium as solid contaminants are collected on the inner surface of the filter medium. Generally such air filter units employ filter cleaning means, such as movable suction nozzles, which transverse the filter medium surface to draw the collected contaminants from the filter medium and convey them to a remote point for disposal. A number of industrial type air filter devices are disclosed in the following U.S. Pat. Nos.:
964,377 PA1 1,497,176 PA1 2,788,860 PA1 3,339,348 PA1 3,345,805 PA1 3,377,780 PA1 3,757,496 PA1 3,864,107 PA1 4,045,194 PA1 4,082,524 PA1 4,154,588
My own prior U.S. Pat. No. 3,887,344 discloses, in particular, a stationary self-cleaning filter drum of cylindrical shape with peripherally disposed filter medium, and a closed end. Air to be filtered is introduced into the interior of the drum through the open end of the drum and passes generally at right angles outwardly through the filter medium as the contaminants therein are collected on the medium. The filtered air leaving the periphery of the drum passes back into the general processing area or it may be directed by suitable ducting to a desired point of use. Collected contaminants are removed from the filter medium by one or more suction nozzles mounted for rotation over the inside surface of the filter medium and connected to a central manifold pipe in the drum. One end of the manifold pipe is connected by a conduit to a suction source and contaminant collection device where the contaminants removed from the system may be suitably disposed of.
Because of the large amount of solid contaminants which are present in the air around certain industrial processing operations, such as in and around textile shearing and napping equipment, a filter drum sized for a particular air flow rate may often become loaded with contaminants faster than the contaminants can be removed from the filter medium surface by the suction nozzles, resulting in clogging of the unit and loss of efficiency of the unit. Obviously, it is desirable to maintain optimum contaminant removal from the air, while maintaining the filter drum and area of the filter medium sized for the desired air flow rate through the system.